This document summarizes Missouri DOT's experience with unbonded concrete overlays. It discusses early projects from the 1930s-1970s and a 1981 survey of those projects. It also outlines current generation unbonded overlay projects since 1986, including "conventional", "big block", and "ultrathin" types. Two specific conventional overlay projects on I-55 and I-44 are described in detail, noting their design, performance, and lessons learned. The document also provides details on two "big block" overlay projects on Route D and US 61, including design, construction methods, and distress survey results.

1. Workshop #3 -
Unbonded Concrete Overlays
Brett Trautman, P.E.
Construction & Materials Div.
Missouri DOT
NRRA Pavement Conference
Albertville, MN
May 23, 2017

2. Overlay Types
 Unbonded Concrete Overlays over
Concrete Pavement
 Unbonded Concrete Overlays over
Asphalt Pavement
 Bonded Concrete Overlays over Asphalt
Pavement (BCOA)
 Bonded Concrete Overlays over Concrete
Pavement (BCOC)

3. Early Beginnings
 Missouri unbonded overlays date back
to 1930s
 21 projects from 1932 to 1970
 First project on US 40 in Callaway
County circa 1932

4. Early Beginnings
 Over 12 miles
paved on US 40 in
Callaway and
Montgomery
Counties
 Projects scattered
all over the state

5. 1981 Survey
 Seven of 21 projects unsurfaced as of 1981
 Overlay thickness from 4“ - 6“
 Half doweled / half undoweled
 Interlayer
- Waterbound select material (1“ - 8“)
- Cutback
- Not sure

6. Current PCC Overlay
Generation
 ~ 20 conventional unbonded concrete
overlay projects constructed since 1986 (all
but 2 since 2000)
- Primarily Interstate
- Nearly all JPCP
- Most ~ 8 inches thick
- Placed over PCCP or composite pavement

7. Current PCC Overlay
Generation
 Six ‘big block’ projects since 2006
 Six ‘ultrathin’ (BCOA) projects since 1999
- All have fibers
 Four bonded PCC overlay (BCOC) projects
since 1990
- No fibers used

9. Approximately 5% of
Missouri Interstate
centerline miles have an
unbonded concrete
overlay.

10. Unbonded Concrete
Overlays
‘Conventional’
1) I-55 in Pemiscot County
2) I-44 in Greene-Webster Counties
Missouri Experience

11. I-55 in Pemiscot County
 First new generation
 Constructed in 1986
 Approximately 7.8 miles in SB lanes
 9“ JRCP, 61.5’ joint spacing - Doweled
 Milled existing AC overlay
 No tied shoulders
 Original PCC ~ 8“

12. I-55 in Pemiscot County

13. I-55 in Pemiscot County
 Overall Performance in 2004
- Ave. IRI = 110 (in/mile)
- Ave. Condition = 19.4 (out of 20)
 Diamond ground in 2006
- Ave. IRI ~ 75 (in/mile)
 Some full depth patching exists

14. I-44 in Greene-Webster
Counties
 First 8“ unbonded JPCP in Missouri
 Constructed in 2000
 Approximately 5.7 miles in WB lanes
 15’ joint spacing - Doweled
 Placed 1“ bondbreaker
 Tied shoulders
 Pavement diamond ground at time of
construction

15. I-44 in Greene-Webster Counties

16. I-44 in Greene-Webster
Counties
 Ave. IRI after construction diamond
grinding = 36.8 (in/mile)
 Recent Performance
- Ave. IRI = 38 (in/mile)
- Ave. Condition = 19.9 (out of 20)
 Very few patches
 Grooved for skid resistance in 2010

17. Lessons Learned

18. Concrete Overlay Issues
Unbonded Concrete Overlay design
thickness – Increase from 8” to 9”
for high volume overlays is
warranted

21. 7.4
7.5
7.6
7.7
7.8
7.9
8.0
8.1
8.2
8.3
8.4
8.5
0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00%
AverageQCCoreThickness(in)
Percent of Slabs Cracked Within QC Lot
Thickness vs. % Cracking

22. Concrete Overlay Issues
Unbonded Concrete Overlay
Interlayer – Stick with geotextile

25. Concrete Overlay Issues
Widened slabs – Probably not a
good idea

26. 2’
widening

27. What
experience
have you had?

28. Unbonded Concrete
Overlays
‘Big Block’
1) Route D in Cass County
- South of Kansas City
2) US 61 in Jefferson County
Missouri Experience

29. Route D in Cass County
 9300 AADT (5 % trucks)
 8-in PCC, 30-ft joints w/ 1-in dowels
 Only 22 years old
- Severely deteriorated by D-cracking
- Estimated 25% of area required full depth
repair prior to conventional HMA overlay

30. Route D in Cass County
 5-inch minimum thickness
 6-foot square panels
 No steel
 No fibers
 Interlayer/Separation Layer Option
- Bituminous Layer
- Geotextile Fabric (selected – first in country
- 2008)

31. Existing Pavement Condition

32. Pre-overlay
repairs
Consist of
bituminous,
cementitious, or other
materials meeting
approval.

33. Fabric
Placement

34. Securing
Fabric

35. Placing and
Finishing
Surface

36. November 2015 Survey
 First thorough visual distress survey
 9768 panels total (3.47 centerline miles)
 69 panels cracked or spalled for 0.7%
failure rate
 Most failures located near northern
transition (@ Rte 150)

37. Route D in Cass County
 November 2015

38. US 61 in Jefferson County
 Composite pavement section south of St.
Louis required rehab.
 Originally scoped for 3 ¾ HMA overlay,
but changed to 5-inch UBOL or ‘big block’
 Constructed in 2009
 6.5’ by 6.5’ joint spacing

39.  Primarily placed directly on existing
composite pavement
 Inlays constructed at transition areas near
bridges and RR approaches and along
side wide, new concrete entrances
 220+ entrances in 12.7 miles!!!!
US 61 ‘Big Block’

41. Utilized Longitudinal Joint
Device Forming

42. Joint Formation

43. February 2016 Survey
 First visual distress survey
 31,840 panels total (~ 10 centerline miles)
 333 panels cracked, spalled or patched for
1.06% failure rate
 2/3 of failures located in northernmost mile

44. 0
20
40
60
80
100
120
140
160 1
201
401
601
801
1001
1201
1401
1601
1801
2001
2201
2401
2601
2801
3001
3201
3401
3601
3801
4001
4201
4401
4601
4801
5001
5201
5401
5601
5801
6001
6201
6401
6601
6801
7001
7201
7401
7601
7801
No. of Distressed Panels on US 61
SB

45. US 61 in Jefferson County
 February 2016

46. US 61 in Jefferson County
 February 2016

47. US 61 in Jefferson County
 February 2016

48. What
experience
have you had?

49. Thank You!!
Brett.Trautman@modot.mo.gov
573-751-1036